Influenza virus (commonly known as "the flu") is a serious disease caused by a virus. Influenza virus can spread from one person to another through small droplets of saliva that are expelled into the air when an infected person coughs or sneezes. The virus can also be passed through contact with objects the infected person has touched, such as a door handle or other surfaces.

Influenza virus vaccine is used to prevent infection caused by influenza virus. The vaccine is redeveloped each year to contain specific strains of inactivated (killed) flu virus that are recommended by public health officials for that year.

The injectable influenza virus vaccine (flu shot) is a "killed virus" vaccine. Influenza virus vaccine is also available in a nasal spray form, which is a "live virus" vaccine.

Influenza virus vaccine works by exposing you to a small dose of the virus, which helps your body to develop immunity to the disease. Influenza virus vaccine will not treat an active infection that has already developed in the body.

Influenza virus vaccine is for use in adults and children who are at least 6 months old.

Becoming infected with influenza is much more dangerous to your health than receiving this vaccine. Influenza causes thousands of deaths each year, and hundreds of thousands of hospitalizations. However, like any medicine, this vaccine can cause side effects but the risk of serious side effects is extremely low.

Like any vaccine, influenza virus vaccine may not provide protection from disease in every person. This vaccine will not prevent illness caused by avian flu ("bird flu").

What is the most important information I should know about this vaccine?

The injectable influenza virus vaccine (flu shot) is a "killed virus" vaccine. Influenza virus vaccine is also available in a nasal spray form, which is a "live virus" vaccine. This medication guide addresses only the injectable form of this vaccine.

Becoming infected with influenza is much more dangerous to your health than receiving this vaccine. However, like any medicine, this vaccine can cause side effects but the risk of serious side effects is extremely low.

What should I discuss with my healthcare provider before receiving this vaccine?

You may not be able to receive this vaccine if you are allergic to eggs, or if you have:

a history of severe allergic reaction to a flu vaccine; or

a history of Guillain-Barre syndrome (within 6 weeks after receiving a flu vaccine).

To make sure influenza virus injectable vaccine is safe for you, tell your doctor if you have:

a bleeding or blood clotting disorder such as hemophilia or easy bruising;

a neurologic disorder or disease affecting the brain (or if this was a reaction to a previous vaccine);

a history of seizures;

a weak immune system caused by disease, bone marrow transplant, or by using certain medicines or receiving cancer treatments; or

if you are allergic to latex rubber.

You can still receive a vaccine if you have a minor cold. In the case of a more severe illness with a fever or any type of infection, wait until you get better before receiving this vaccine.

The Centers for Disease Control and Prevention recommends that pregnant women get a flu shot during any trimester of pregnancy to protect themselves and their newborn babies from flu. The nasal spray form of influenza vaccine is not recommended for use in pregnant women.

It is not known whether influenza virus vaccine passes into breast milk or if it could harm a nursing baby. Do not receive this vaccine without telling your doctor if you are breast-feeding a baby.

This vaccine should not be given to a child younger than 6 months old.

How is this vaccine given?

Some brands of this vaccine are made for use in adults and not in children. Your child's doctor can recommend the best influenza virus vaccine for your child.

This vaccine is given as an injection (shot) into a muscle. You will receive this injection in a doctor's office or other clinic setting.

You should receive a flu vaccine every year. Your immunity will gradually decrease over the 12 months after you receive the influenza virus vaccine. Children receiving this vaccine may need a booster shot one month after receiving the first vaccine.

The influenza virus vaccine is usually given in October or November. Some people may need to have their vaccines earlier or later. Follow your doctor's instructions.

Your doctor may recommend treating fever and pain with an aspirin-free pain reliever such as acetaminophen (Tylenol) or ibuprofen (Motrin, Advil, and others) when the shot is given and for the next 24 hours. Follow the label directions or your doctor's instructions about how much of this medicine to give your child.

It is especially important to prevent fever from occurring in a child who has a seizure disorder such as epilepsy.

What happens if I miss a dose?

Since flu shots are usually given only one time per year, you will most likely not be on a dosing schedule. Call your doctor if you forget to receive your yearly flu shot in October or November.

If your child misses a booster dose of this vaccine, call your doctor for instructions.

What happens if I overdose?

An overdose of this vaccine is unlikely to occur.

What should I avoid before or after receiving this vaccine?

Follow your doctor's instructions about any restrictions on food, beverages, or activity.

Influenza virus injectable vaccine side effects

Influenza virus injectable (killed virus) vaccine will not cause you to become ill with the flu virus that it contains. However, you may have flu-like symptoms at any time during flu season that may be caused by other strains of influenza virus.

You should not receive a booster vaccine if you had a life-threatening allergic reaction after the first shot.

Keep track of any and all side effects you have after receiving this vaccine. If you ever need to receive influenza virus vaccine in the future, you will need to tell your doctor if the previous shot caused any side effects.

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

a light-headed feeling, like you might pass out;

severe weakness or unusual feeling in your arms and legs (may occur 2 to 4 weeks after you receive the vaccine);

high fever;

seizure (convulsions); or

unusual bleeding.

Common side effects may include:

low fever, chills;

mild fussiness or crying;

redness, bruising, pain, swelling, or a lump where the vaccine was injected;

headache, tired feeling; or

joint or muscle pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report vaccine side effects to the US Department of Health and Human Services at 1-800-822-7967.

What other drugs will affect influenza virus injectable vaccine?

Before receiving this vaccine, tell your doctor if you are using:

phenytoin;

theophylline; or

a blood thinner such as warfarin, Coumadin.

Also tell the doctor if you have recently received drugs or treatments that can weaken the immune system, including:

an oral, nasal, inhaled, or injectable steroid medicine;

medications to treat psoriasis, rheumatoid arthritis, or other autoimmune disorders--azathioprine, etanercept, leflunomide, and others; or

If you are using any of these medications, you may not be able to receive the vaccine, or may need to wait until the other treatments are finished.

This list is not complete. Other drugs may affect influenza virus injectable vaccine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed in this medication guide.

Professional resources

Related treatment guides

Where can I get more information?

Your doctor or pharmacist can provide more information about this vaccine. Additional information is available from your local health department or the Centers for Disease Control and Prevention.

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Disclaimer: Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.